Polymer leaching from film coating: Effects on the coating transport properties.

Mariagrazia Marucci, Gert Ragnarsson, Christian von Corswant, Anette Welinder, Annica Jarke, Frida Iselau, Anders Axelsson

Research output: Contribution to journalArticlepeer-review


The release mechanism of metoprolol succinate pellets coated with a blend of a water-insoluble polymer, ethyl cellulose (EC), and a water-soluble polymer, hydroxypropyl cellulose (HPC) is mechanistically explained. The kinetics of drug release and HPC leaching were followed for drug doses. The coating was initially not permeable to the drug, and release started only after a critical amount of the HPC had been leached out. Drug release occurred mainly through pores created in the coating by the HPC dissolution. Single-pellet release experiments were also performed. The coating thickness and size of each pellet were measured. In order to quantitatively characterize the transport properties of the coating of the individual pellets, and to determine the effective diffusion coefficient (D(e)) of the drug in the coating, a mechanistic model was used to fit the single-pellet release data. It was found that D(e) increased with time due to an increase in the amount of HPC leached. It was also found that D(e) was dependent on the coating thickness, and increased more slowly with a thicker coating. This agreed well with the finding that the HPC leaching rate decreased with increasing film thickness.
Original languageEnglish
Pages (from-to)43-48
JournalInternational Journal of Pharmaceutics
Publication statusPublished - 2011

Subject classification (UKÄ)

  • Chemical Engineering


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